/************************************************************************
                                                                     
   Xceed Ultimate ListBox for Silverlight                                                                                                                                            
   Copyright (C) 2010 Xceed Software Inc.    
                                                                     
   This program is provided to you under the terms of the GNU General Public  
   License version 2 as published by the Free Software Foundation. 
        
   This program is distributed in the hope that it will be useful, but
   WITHOUT ANY WARRANTY, without even the implied warranty of 
   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
   General Public License for more details.

   You should have received a copy of the GNU General Public License along 
   with this program, if not, write to the Free Software Foundation, Inc., 
   51 Franklin Street, Fifth Floor, Boston, MA  02110-1301, USA.

   This program can be provided to you by Xceed Software Inc. under a
   proprietary commercial license agreement for use in non-Open Source
   projects. Visit Xceed.com to find the commercial edition of 
   Xceed Ultimate ListBox for Silverlight.                                    
                                                                      
 **********************************************************************/

using System;
using System.Collections;
using System.Collections.Generic;
using System.ComponentModel;
using System.Diagnostics;
using System.Linq;
using System.Linq.Expressions;

namespace Xceed.Silverlight.Data
{
  internal class LocalListEnumerator<T> : SyncEnumerator<T>
  {
    public LocalListEnumerator( List<T> dataList )
    {
      if( dataList == null )
        throw new ArgumentNullException( "dataList" );

      m_dataList = dataList;
    }

    protected virtual List<T> DataList
    {
      get
      {
        return m_dataList;
      }
    }

    private int LimitBounds( List<T> items, long index )
    {
      return Convert.ToInt32(
               Math.Max(
                 -1,
                 Math.Min( Convert.ToInt64( items.Count ), index ) ) );
    }

    public override CountResult Count( CountParameters parameters )
    {
      FilterExpressionBase filter = null;
      if( ( parameters.StartPosition != null ) && ( parameters.StartPosition.SortingReference.Count > 0 ) )
      {
        IList<object> values = parameters.StartPosition.SortValues;
        IList<SortDescription> sortOrder = parameters.StartPosition.SortingReference.Take( values.Count ).ToList();

        if( parameters.CountChildOnly )
        {
          filter = NavigationFilterUtils.CreateFilterExpression( sortOrder, values );
        }
        else
        {
          bool includeStartingItem = ( parameters.StartPosition.StartPosition == StartPosition.Before );

          filter = NavigationFilterUtils.CreateFilterExpression( sortOrder, values, false, includeStartingItem );
        }
      }

      IEnumerable<T> dataSource = m_dataList;
      if( filter != null )
      {
        PredicateBuilder pb = new PredicateBuilder( filter );
        Func<T, bool> predicate = pb.ToPredicate<T>();

        dataSource = dataSource.Where( predicate );
      }

      return new CountResult( dataSource.Count() );
    }

    public override GroupCountResult GroupCount( CountParameters parameters )
    {
      Debug.Assert( false, "not expected to be used" );

      return new GroupCountResult( null );
    }

    public override StatResults GetStatValues( StatParameters parameters )
    {
      Debug.Assert( false, "not expected to be used" );

      throw new DataInternalException();
    }

    public override bool JumpMoveAndFetch(
      JumpMoveAndFetchParameters parameters,
      out Nullable<long> actualMoveCount,
      out ICollection<T> fetchedItems,
      out SourcePosition endPosition,
      out RelativeOffset endPositionOffset,
      out EstimateInt64 totalCount )
    {
      SourcePosition sourcePosition = parameters.SourcePosition;
      long expectedMoveCount = parameters.ExpectedMoveCount;
      int expectedFetchCount = parameters.ExpectedFetchCount;

      this.CheckMoveAndFetchParameters( expectedMoveCount, expectedFetchCount );

      List<T> dataList = this.DataList;
      int queryDirection = ( expectedMoveCount != 0 ) ? DataUtils.GetUnit( expectedMoveCount ) : DataUtils.GetUnit( expectedFetchCount );
      int sourcePositionIndex = this.FindSourcePositionIndex( sourcePosition, parameters.ExpectedMoveCount, parameters.ExpectedFetchCount );
      int moveResult = this.MoveIndex( dataList, sourcePositionIndex, expectedMoveCount );

      actualMoveCount = moveResult - sourcePositionIndex;
      totalCount = dataList.Count;

      if( moveResult == -1 || moveResult == dataList.Count )
      {
        fetchedItems = null;
        if( moveResult == -1 )
        {
          endPosition = SourcePosition.BeforeFirst;
          endPositionOffset = new RelativeOffset( 0, ReferencePoint.BeforeFirst );
        }
        else
        {
          endPosition = SourcePosition.AfterLast;
          endPositionOffset = new RelativeOffset( 0, ReferencePoint.AfterLast );
        }
      }
      else
      {
        IList<T> fetchResult = this.Fetch( dataList, moveResult, expectedFetchCount );

        fetchedItems = fetchResult;
        Debug.Assert( fetchResult != null );
        Debug.Assert( ( fetchResult.Count == 0 ) == ( expectedFetchCount == 0 ) );

        if( fetchResult.Count != Math.Abs( expectedFetchCount ) )
        {
          if( DataUtils.GetUnit( expectedFetchCount ) == 1 )
          {
            endPosition = SourcePosition.AfterLast;
            endPositionOffset = new RelativeOffset( 0, ReferencePoint.AfterLast );
          }
          else
          {
            endPosition = SourcePosition.BeforeFirst;
            endPositionOffset = new RelativeOffset( 0, ReferencePoint.BeforeFirst );
          }
        }
        else
        {

          if( fetchResult.Count == 0 )
          {
            endPosition = new ItemPosition( dataList[ moveResult ] );
            endPositionOffset = new RelativeOffset( moveResult + 1, ReferencePoint.BeforeFirst );
          }
          else
          {
            endPosition = new ItemPosition( fetchResult[ fetchResult.Count - 1 ] );
            endPositionOffset = new RelativeOffset( dataList.IndexOf( fetchResult[ fetchResult.Count - 1 ] ) + 1, ReferencePoint.BeforeFirst );
          }
        }
      }

      return ( actualMoveCount == expectedMoveCount ) && ( fetchedItems != null ) && ( fetchedItems.Count == Math.Abs( expectedFetchCount ) );
    }

    protected virtual int FindSourcePositionIndex( SourcePosition sourcePosition, long expectedMoveCount, int expectedFetchCount )
    {
      if(sourcePosition.IsBeforeFirst)
        return -1;

      if(sourcePosition.IsAfterLast)
        return this.DataList.Count;

      if(sourcePosition is ItemPosition)
      {
        T item = (T) ((ItemPosition)sourcePosition).Item;
        int itemIndex = this.GetItemIndex(item);

        Debug.Assert(itemIndex != -1, "Inconsistent data source");
        return itemIndex;
      }

      throw new DataInternalException();
    }

    protected virtual int GetItemIndex(T item)
    {
      return this.DataList.IndexOf(item);
    }

    protected int MoveIndex( List<T> list, int initialIndex, long expectedMoveCount )
    {
      return this.LimitBounds( list, initialIndex + expectedMoveCount );
    }

    protected IList<T> Fetch( List<T> fetchedList, int firstFetchedIndex, int expectedFetchCount )
    {
      if( fetchedList == null )
        throw new ArgumentNullException( "fetchedList" );

      if( firstFetchedIndex < 0 || firstFetchedIndex >= fetchedList.Count )
        return null;

      if( expectedFetchCount == 0 )
        return new List<T>( 0 );

      int endFetchIndex = this.LimitBounds( fetchedList, firstFetchedIndex + expectedFetchCount );
      int fetchedIndex = ( firstFetchedIndex <= endFetchIndex ) ? firstFetchedIndex : endFetchIndex + 1;
      int fetchedCount = Math.Abs( endFetchIndex - firstFetchedIndex );

      List<T> fetched = fetchedList.GetRange( fetchedIndex, fetchedCount );

      if( DataUtils.GetUnit( expectedFetchCount ) == -1 )
      {
        fetched.Reverse();
      }
      return fetched;
    }

    private List<T> m_dataList;
  }
}
